PAUT transducers typically comprise a piezoelectric ceramic transducer array, with conductive elements deposited on the ceramic for making electrical contact with each transducer of the array, a backing material for acoustic damping and an electric circuit with pins for making contact with the conductive elements. The pins and electric circuit are often in the form of flexible printed circuit boards (PCBs). The conductive elements are formed from a thin film of conductive material, such as gold, which may be deposited by any suitable deposition method, such as sputtering, the film being patterned so that each conductive element is in electrical contact with one transducer of the array.
In existing practice, PAUT transducer assembly methods involve using soldering to attach the flexible circuit to the conductive elements. Soldering, even with a high level of automation, is typically time and labor consuming, which slows productivity.
In addition, soldering used in the PAUT industry for transducer manufacturing largely involves lead soldering. By 2017 the industry is required to be Restriction of Hazardous Substance (ROHS) compliant in order to ship product to the European Union. Consequently, lead free manufacturing will be required for this application.
Thus, there has been a need for an assembly process for making PAUT probes that can achieve precise, firm and permanent contacts between the PCB and the piezoelectric without using soldering.